Generally, integrated circuits (ICs) comprise electronic components, such as transistors, capacitors, or the like, formed on a substrate. One or more metal layers are then formed over the electronic components to provide connections between the electronic components and to provide connections to external devices. The metal layers typically comprise an inter-layer dielectric (ILD) layer in which interconnect structures, such as vias and conductive traces, are formed, usually with a single- or dual-damascene process.
The trend in the semiconductor industry is towards the miniaturization or scaling of integrated circuits, in order to provide smaller ICs and improve performance, such as increased speed and decreased power consumption. While aluminum and aluminum alloys were most frequently used in the past for the material of conductive lines in integrated circuits, the current trend is to use copper for a conductive material because copper has better electrical characteristics than aluminum, such as decreased resistance, higher conductivity, and a higher melting point.
The change in the conductive line material and insulating materials of semiconductor devices has introduced new challenges in the manufacturing process. For example, copper oxidizes easily and has a tendency to diffuse into adjacent insulating materials, particularly when a low-K material or other porous insulator is used for the ILD layer. To reduce these effects, attempts have been made to form a cap layer comprising a single layer of CoWP and CoB over the copper material. While the CoWP and CoB cap layers help reduce the oxidation and diffusion of the copper into the surrounding ILD layer, the CoWP and CoB cap layers require numerous processing steps and often result in metal residue on the surface of the ILD layer. These cap layers also exhibit poor resistance to oxygen and other chemicals, which may result in Rc yield loss and high contact resistance.
Accordingly, there is a need for a cap layer that eliminates or reduces surface migration and diffusion of the conductive material into adjacent insulating materials while being easily and efficiently formed.